Chris Marshall

When a story appeared in a Sunday newspaper in April 2015 about the 2005 murder of Emma Caldwell, police knew the provider of the information had to be someone with knowledge of the long-running investigation.

Police Scotland’s counter-corruption unit (CCU) swung into action to find the source of the leak, eventually falling foul of guidelines – at that point only recently introduced – which seek to protect journalists from police intrusion without judicial approval.

Those officers who overstepped their remit can have had little idea where things would end up.

On Monday, Derek Penman, HM Inspectorate of Constabularly in Scotland, released an interim report as part of his review of Police Scotland’s counter-corruption tactics.

It essentially called for root and branch reform of how the CCU operates, making a total of 39 recommendations for improvements.

The newspaper article which kicked all this off was about a “forgotten suspect” in the hunt for Emma Caldwell’s killer.

The 27-year-old heroin addict had been working as a prostitute when her body was discovered in woodland near Biggar, South Lanarkshire, more than a decade ago. The 2015 article, which appeared in the Sunday Mail, and subsequent articles led the Lord Advocate to demand the murder be re-investigated.

It’s an example of how serious investigative journalism can make a real impact.

But those journalists involved in the piece, or at least their source, found themselves the subject of a police witch hunt.

Last year the Interception of Communications Commissioner’s Office (IOCCO) said Police Scotland had been “reckless” in failing to obtain judicial approval when attempting to access communications data relating to the case.

The IOCCO investigation related to use of the controversial Regulation of Investigatory Powers Act (Ripa), which allows authorities to ask for the “who”, “when” and “where” of phone or e-mail communication, but not its content.

Sir Stanley Burnton, the Interception of Communications Commissioner, said Police Scotland had sought communications data to determine a journalist’s source or the “communications of those suspected to have been acting as intermediaries between a journalist and a suspected source”.

In his report, Mr Penman said CCU information-handling processes were “significantly different from national standards for source and information evaluation, and fell below the standards I would have expected”.

He found CCU safeguards for managing contact with police sources were “inadequate” and criticised the handling of CCTV disc footage that led to evidence being lost.

The review concluded the unit had become “largely reactive” with “minimal evidence of proactive anti-corruption investigations”.

Mr Penman also highlighted concerns about the “legality, proportionality and the apparent lack of procedural fairness carried out by the CCU when dealing with police officers and members of police staff”.

The highly secretive Investigatory Powers Tribunal is due to discuss the CCU case next month.

By then an overhaul of the controversial unit may already be under way.